1. Field of the Invention
The invention relates generally to automatic guidance systems and more specifically to global positioning system based apparatus for guiding the operation of movable machinery.
2. Description of the Prior Art
Movable machinery such as open-pit mining machines and airplane crop dusters alike can all benefit from decimeter-level accurate global positioning system (GPS) high-precision survey products, e.g., as sold commercially by Trimble Navigation (Sunnyvale, Calif.), and others. But such environments are very hostile, especially to delicate electronic instruments such as land surveying equipment that is usually human-mounted, rather than machine mounted. Earth moving machines are subject to all forms of chemical and mechanical injury. Diesel fuel, hydraulic fluid and even mud slurry can invade every crevice and corner of a machine, and such occurrences are common on a regular basis. Trees, rocks, earth and tools can drop at any time on instruments attached to earth-moving equipment. Engine vibration is severe in such equipment and crop duster airplanes as well.
Equipping such vehicles to benefit from GPS systems involves far more that just mounting an ordinary system to a new platform.
The operation of an airplane, especially in crop dusting service, and the operation of heavy equipment, especially in open pit mines, are far beyond what an automatic control system could pilot unmanned. Therefore, the human operator is still an indispensable part of such activities. It is incumbent then on a guidance system to provide an easy and effective indication of how the machine is deviating from the plan from moment to moment.